European Council President Donald Tusk gives one of the starkest warnings yet from the European Union against hostile foreign meddling in May’s European Parliament elections.

Speaking at a news conference on Tuesday, Tusk urged voters across Europe not to allow anti-European parties set up by hostile external forces to use the upcoming parliamentary elections to seize influence in Brussels.

“There are external anti-European forces which are seeking - openly or secretly - to influence the democratic choices of the Europeans,” Tusk said, naming the “Leave” result in Britain’s 2016 Brexit referendum as one such example.

“And it may again be the case with the European Parliament election in May. Do not allow political parties that are founded by external forces hostile to Europe to decide on key priorities of the EU and the leadership of European institutions,” he added.

Anti-EU political parties have surged across the continent, particularly after the 2015-2016 immigration crisis that saw hundreds of thousands of asylum seekers across the 28-nation bloc.

Tusk’s native state, Poland, and Hungry, Italy and Austria have witnessed the rise of nationalists that are seen as a threat to the entirety of the European Union.

Tusk, a center-right former Polish prime minister who chairs summits of EU leaders, also commended some reforms by French President Emmanuel Macron, who has proposed greater cooperation among Europeans in what he calls a “Renaissance of Europe."

“We cannot wait for the renaissance of Europe. The renaissance of Europe must start now,” Tusk said.

Macron has proposed the establishment of a new European agency that would be charged with protecting democracy, to safeguard the EU from cyber attacks and propaganda that undermine its elections and from foreign funding of political parties.

The French president has also suggested the formation of bloc-wide agencies to deal with borders, security and asylum, and issues such as food safety.

Back in February, Tech giant Microsoft said it had detected hacker "attacks" ahead of European Parliament and national elections in the EU, in a warning to civil society groups, politicians and campaigns.